EXCRETION OF WASTE PRODUCTS 187 



The source of the creatinine is not definitely known. Muscle 

 contains creatine, and it has been suggested that the constancy 

 of the creatinine output is dependent on the amount of 

 muscle in the body. 



Creatinine is formed from creatine by dehydration, usually 

 carried out in vitro by heating with acid. 



The liver has been suggested as the seat of transformation 

 of creatine into creatinine.* If the creatinine is an indication 

 of muscular metabolism it is related to the metabolism 

 independent of contraction, as muscular movements do not 

 increase the amount of creatine in muscle nor creatinine in 

 urine. 



/NH 



N = NH N = NH 



^N CH 3 COOH >N CH 3 CO 



CH 8 CH 3 



Creatine. Creatinine. 



Creatine is not usually found in the urine, but it occurs 

 in the urine of children, | in the urine of women under certain 

 conditions, such as menstruation and pregnancy, J and in the 

 urine during starvation. Cathcart has found that the adminis- 

 tration of sugar abolishes the excretion of creatine in fasting 

 individuals. 



Creatine is a normal constituent of the urine of birds. || 

 Cathcart suggests that the presence of sugar allows the 

 creatine formed by tissue breakdown to be reformed into the 

 structures of the tissues. In the absence of sugar the tissues 

 are decomposed and the non-nitrogenous portion used for 

 energy transformations. The creatine thus set free appears 

 in the urine. If sugar is present the creatine is reformed into 

 tissue material. This result would follow from the law of 

 mass action and can be expressed by the equation on p. 57. 

 The reversible process can be understood to be as follows : 



protein Sugar 



Muscle tissue ^IZ^ and ^~ amino acids 

 creatine 



I 

 excreted. 



* E. Mellanby, Journ. PhysioL, 1908, vol. 36, p. 447. 



f O. Folin and W. Denis, Journ. Biol.Chem., 1912, vol. n, p. 253. 



J R. A. Krause, Quart. Journ. Exper. PhysioL, 1911, vol. 4, p. 293. 



E. P. Cathcart, Journ. PhysioL, 1909, vol. 39, p. 311. 



|| D. Noel Paton, Journ. PhysioL, 1909, vol. 39, p. 485. 



